1. Field of the Invention
The subject invention generally relates to dock levelers, and more specifically, to dock levelers having a lip extension.
2. Description of Related Art
Dock levelers are used to compensate for height differences between a loading dock platform and an adjacent bed of a truck or trailer. A typical dock leveler includes a deck, also known as a ramp or dockboard, which is pivotally hinged along its back edge to vary the height of its front edge. An extension plate, or lip, extends outward from the deck's front edge to span the gap between the rear of the truck bed and the front edge of the deck. The lip is usually moveable between a retracted, stored position (i.e., clear of the truck) to an extended, operative position. In the extended, operative position, the lip extends from the deck's front edge and rests upon the truck bed to form a bridge between the two. This allows personnel and material handling equipment to readily move on and off the vehicle during loading and unloading operations.
With some dock levelers, the lip moves linearly, as disclosed in U.S. Pat. No. 6,081,954 and German Patent DE2800128A1. The linear movement allows varying the extent to which the front edge of the lip overlaps the vehicle bed. A variable overlap can be useful when cargo rests particularly near the rear edge of the vehicle bed, and thus limits the bed's available floor space upon which the front edge of the lip may rest. In such cases, the operator may move the lip linearly up against the cargo. But this could create dangerously insufficient overlap between the lip and the truck bed; as such an approach relies on the operator's judgment. Too small of an overlap could result in loss of contact between the lip and the bed—potentially allowing the deck to fall. Another dock leveler, disclosed in German Patent DE19612135A1, has a lip fixed relative to its deck with side bumpers that move along a plane. However, all of these devices in their stored positions (also known as a cross-traffic position where an upper surface of the deck is flush with the adjacent floor) provide no significant obstruction to a forklift or other material handling equipment that might accidentally drive off the front edge of the deck when a vehicle is not present at the dock.
However, some dock levelers include a pivotal lip with a rear edge that protrudes above the deck when the deck is in its cross-traffic position, thereby providing an obstruction to material-handling equipment. During loading or unloading operations, a front edge of the lip pivots out over the rear edge of the truck bed, while the rear edge of the lip pivots down to overlap the deck, thus bridging the gap between the deck and the truck bed while removing the obstruction to material-handling equipment. But the extension of the lip is generally fixed, so the lip is unable to adjust to situations where there is limited floor space at the rear of a vehicle bed.
Another dock leveler, disclosed in U.S. Pat. No. 4,920,598, provides a pivoting lip with some sliding movement when the lip hangs generally pendant. In the stored, cross-traffic position, the sliding movement allows the lip to protrude above the deck. The protruding portion of the lip thus creates an obstruction that helps inhibit equipment from accidentally driving off the front edge of the deck. When the deck is raised from the cross-traffic position, the sliding movement allows the lip 30 to translate relative to the deck to a position where the rear or top edge of the lip no longer forms an obstruction. The lip can then be extended to a position where the rear edge of the lip abuts the front edge of the deck, thus preventing the lip from sliding back. Thus, cargo at the very back of the truck bed may interfere with a fully extended lip. So in such cases, the lip is moved to a substantially pendant position below the deck, and the deck is either moved to its cross-traffic position or to a below-dock position. In the cross-traffic position the deck is generally flush with the adjacent floor of the dock platform, and in the below-dock position, the deck is below the adjacent floor. In either case, the lip does not rest on the bed of the truck nor does it protrude above the deck. This allow some material-handling equipment, such as fork lift trucks, to drive onto the deck and reach out with their forks to place or remove loads from the very rear of the truck bed without interference from the lip. However, the gap between the deck and the truck bed (due to the lip being pendant) is generally not meant to be driven across. Thus, the gap inhibits some material handling equipment, such as pallet jacks, from loading or unloading cargo from the very rear of the vehicle bed.